In magnetic memory disks, information is recorded in concentric tracks on both sides of a disk. Read/write heads are moved to a particular track to gain access to the information recorded in that track. The tracks on a side of a magnetic disk are extremely closely fit, making it difficult to meet the requirement for high-speed movement of a read/write head. Head movement may be considered in two aspects: (1) track seeking and location; (2) movement into or out of a magnetic flux coupling relation with the disk surface on a track. The present invention deals mainly with the second aspect, but this aspect has an effect on the first aspect. Requirement of head movement within a 15 microsecond time window is typical for both aspects.
Track seeking is often provided by a linear actuator which moves the heads radially along the disk. Thus, the heads and the carriage which supports the heads move across the disk in a straight line manner. Rotary actuators are also used for track seeking. A rotary actuator mounts the heads at the end of an arm assembly which is pivoted at an end opposite the heads. The heads are then moved about the maximum radius of the apparatus so that higher acceleration can be gained for quick access to the desired information. Moreover, the end of the arm supporting the heads presents less inertial resistance to movement, thereby permitting rapid acceleration between positions. The present invention may be used with either type of actuator.
In the recordation of data on the disk, read/write heads are brought into data transfer engagement with opposed surfaces of the memory disk, by close spacing of the head to the disk, so that magnetic flux from the head can influence magnetic domains on the disk. Information is then recorded in various tracks on the opposed surfaces. Rapid acceleration and deceleration is imperative since head movement must take place within a specific time window. Simultaneously, accuracy is critical because the heads must be positioned and then repositioned at the same spot with a high degree of repeatability. During repositioning of the read/write heads, the heads are supported on the disk by a film of air which prevents contact between the heads and the disk. Direct contact of the disk with a head may result in damage to either or both of the head and disk, as well a loss of information. The film of air acts as an air cushion for a head and results from rotation of the disk at high speeds. After verifying that a magnetic memory disk will accept information, the read/write heads are removed from the disk into an unload position.
Assemblies for loading and unloading of magnetic heads are known. The terms "loading" and "unloading" mean bringing the head into and out of magnetic communication with the disk so that data can be read or written. This operation can be separate from or simultaneous with a track seeking operation. Typically, load-unload assemblies in large drives utilize a position slidably fit within an air cylinder. A danger which must be addressed in all load-unload assemblies is that of head crash with the magnetic disk. Dampening devices are therefore used to control the speed at which a head approaches a magnetic disk.
It is not uncommon in actuators to find that movement of a read/write head requires displacement of not only the head but also the carriage, a load-unload piston and cylinder assembly, and a dampening device. Movement of a large mass, however, is not advantageous to optimal operation of an actuator. A large mass provides an inertial resistance that inhibits rapid acceleration and deceleration and track-to-track repositioning of the read/write head. Moreover, an increase in mass leads to an increase in the occurrence of ringing, i.e. oscillation of the heads following deceleration. Ringing is detrimental to the efforts to minimize the time required for head repositioning.
The object of the present invention is to provide an actuator to be used in memory disk operations which significantly reduces the mass that must be displaced in track-to-track repositioning of a read/write head. Another object is to provide such an actuator having a load-unload device that reduces the risk of head crash.